Applications

dawn/apps directory includes example Dawn applications. They can be used as an out of the box solution, or they can be a guide for the user to implement their own custom application.

dawn

The default dawn application uses dynamic allocation to create objects.

Not the best solution for small systems or applications where we want to avoid dynamic allocation.

Customizing the default app

The default app is extended without forking dawn_main.cxx via the weak-symbol hooks declared in <dawn/oot.hxx>. Out-of-tree projects provide strong overrides in <oot>/external/dawn_oot_hooks.cxx, which the build attaches to apps_dawn through dawn_oot_user_setup_app(). Two groups of hooks are available:

User factories

user_io_factory / user_prog_factory / user_proto_factory let the project supply custom IO / PROG / PROTO classes. apps_dawn calls all three at startup and passes the results into CDawn. The handler consults the user factory first, then falls back to the built-in factory, so a user factory only needs to handle the class IDs it owns. Reuse a built-in class ID to override the default implementation, or pick an ID in the user-reserved range (IO_CLASS_USER 500, PROG_CLASS_USER / PROTO_CLASS_USER 511) to add a brand-new type. See Customization and Out-of-Tree API Reference for the full recipe.

App lifecycle hooks

user_init, user_post_load, user_on_idle and user_pre_shutdown run custom code at startup, after descriptor load, on each main-loop tick, and before teardown. See App lifecycle hooks in the customization guide for signatures and failure semantics.

Descriptor Source Modes

dawn supports two descriptor source approaches selected by Kconfig.

YAML descriptor (recommended)

Use YAML as source of truth and generate C++ descriptor during build.

Required Kconfig options:

CONFIG_DAWN_APPS_EXAMPLE_DESC_FORMAT_YAML=y
CONFIG_DAWN_APPS_EXAMPLE_DESC_YAML_PATH=".../descriptor.yaml"

Build flow:

CMake runs dawnpy descriptor generator.
Generated file is written to build directory as generated_descriptor.cxx.
dawn_descriptor.cxx includes generated file in compilation.

Legacy C++ descriptor

Use pre-generated static C++ descriptor file.

Required Kconfig options:

CONFIG_DAWN_APPS_EXAMPLE_DESC_FORMAT_CXX=y
CONFIG_DAWN_APPS_EXAMPLE_DESC_PATH=".../descriptor.cxx"

This mode is still supported for compatibility, but YAML mode is the recommended default for board configurations.

dawn_static

An idea for an application where objects are created statically. Not implemented yet, just an idea for the future.